Most large vehicles typically utilize braking systems that include air-pressure or hydraulic-actuated technologies. Such systems typically include a brake actuator which includes an air pressure cylinder that is mechanically linked to the brake by a push rod attached to a piston. This mechanical linkage exhibits travel which increases as the braking member, such as brake pad or brake lining, wears during use. In typical large vehicle applications, the actuator is visible upon inspection. It is thus common to evaluate the magnitude of brake wear by observing the degree of travel of the actuator rod relative to more stationary portions of the system or the vehicle. The degree of travel can be evaluated by comparing marks on the rod in its most retracted position within the cylinder with the length of extension of the push rod as the brake is applied. Most vehicle standardization codes provide a permissible limit to the magnitude of travel of actuator rod.
In rail car systems, in particular, it is often difficult to visually inspect the braking system by determining the degree of travel of the brake actuator push rod. Typically, such inspection requires additional equipment that must be utilized in difficult-to-reach places such as the underside of the rail car between rails. Furthermore, dirt, snow and ice accumulation underneath the rail car may prevent effective viewing of the push rod to determine accurately the proper degree of travel. This leads to the problem of inspections taking place less frequently than required, which can be a serious safety concern. Furthermore, such labor-intensive inspections require the use of valuable and sometimes expensive personnel who would be better-suited for other duties.